1. Field of Invention
The present invention relates to a communication system, and more particularly to a GPS-microphone for a communication system, wherein the GPS-microphone is capable of sending out positioning data in form of audio signals to a control center such that the GPS-microphone supports both the communication provision and the position location provision.
2. Description of Related Arts
Communication devices, such as cellular phone, satellites phone, PDA, and “Pocket PC”, are considered as one of the common communication tools that a user is able to wirelessly communicate with another user through the communication device via a public network. A kind of conventional communication device generally comprises a microphone speaker and a wireless (codec) modem such as RF transmitter/receiver connected with the microphone speaker in such a manner that when the microphone speaker receives an audio signal, the audio signal is encoded to a digital data and sent out in a wireless manner.
Generally speaking, a two-way radio system is considered as one of the most common low-end communication devices, wherein the two-way radio communication system comprises a remote user sending and receiving voice communications to a user at a base station location along a pre-established communications channel. Those communications are half-duplex in nature whereby a user asserts a Push-To-Talk (PTT) switch associated with the radio to transmit a message, otherwise the radio is in receive mode listening for messages when the switch is not asserted. In many scenarios, a detachable corded hand-held microphone unit is used with the radio which the user primarily uses to send and receive voice communications via the radio. The microphone unit has its own PTT switch which controls the radio transmit/receive mode.
The interface between the radio and the handheld microphone unit in this scenario typically comprises a PTT signal from microphone unit to radio, a mic-audio from microphone unit to radio, a speaker audio from radio unit to microphone unit, a ground return from microphone unit to radio, and a optional DC Offset voltage from radio unit to microphone unit.
With PTT asserted, the mic-audio signal from the microphone unit is passed as a baseband signal to the radio which performs conditioning, modulation, and RF signal transmission to complete the transmit steps. With PTT de-asserted, the radio serves to receive the RF signal transmission, demodulate and condition, and then to send the baseband signal as speaker audio to the microphone unit.
Nowadays, the conventional communication devices can be incorporated with a Global Positioning System (GPS) for tracking the location of the user, wherein the common GPS generally comprises a built-in GPS receiver equipped with the modem to wirelessly send out a positioning data from the communication device. In order to receive the GPS positioning data, the communication device must employ a processor unit arranged in such a manner that after the processor unit receives the positioning data, the positioning data is decoded to a readable data so that the user is able to locate the position of the sender.
However, such GPS incorporated communication device has several drawbacks. The communication device must be employed with the modem for wirelessly transmitting both the audio signal and the positioning data, which will highly increase its manufacturing cost. Furthermore, the data transmission speed of the modem is inconsistent such that there is always a delay when both the audio signal and the positioning data are sent out.
In addition, existing lower-end radio systems do not support position location provisions, although providing a remote user's position to a base station would be very desirable to enable tracking of the remote user, particularly through the use of the Global Positioning Satellite (GPS) system. Therefore, the GPS must be independently installed to provide positioning data.
For example, while patrolling, police officers or security officers generally must arm with a radio frequency communication device to keep contact with the control center. For safety and arrangement purpose, their locations are preferred to be tracked by the control center so that the control center can give assistance to them in case of emergency. However, the police officers or the security officers must carry an additional GPS device in order to send out the positioning signals to the control center. In other words, the additional GPS device will increase the load of the police officers or the security officers while patrolling.